I don't quite see how this is a plugin issue. From what I see the problem is in Trac itself where any upgrade will call the backend backup routine, which from what I read from the traceback factors out to subprocess.Popen(). This is basically regular shell tools, and it likely don't find the necessary tools as the local machine does not have mysql installed.
Anyway, my guess is that any plugin that needs upgrades will crash the same way. I suggest you make a db copy manually, and then turn off backup on the trac-admin upgrade command using the --no-backup (or -b) option when running.
Please reopen ticket if I got this all wrong.
